In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Among the entities, try to find the best entity that is most likely to fill in "_" and classify the answers based on options.
Q: A smartphone gadget could help thousands of patients self-diagnose in seconds – and without setting foot in a hospital – a serious heart condition that causes strokes. The new AliveCor heart monitor picks up abnormal heart rhythms in much the same way an electrocardiogram (ECG) machine in a hospital records the electrical activity of the heart. Results are then delivered to an app, which alerts the patient if they have a normal or abnormal heart rhythm. The results can then be emailed or printed out to take to a GP. The device, which costs £65, has been hailed as a ‘game-changer’ in detecting atrial fibrillation (AF), a condition that affects up to 1.8 million Britons and is a major cause of stroke.The new AliveCor heart monitor picks up abnormal heart rhythmsWorks in same way an electrocardiogram (ECG) machine in hospitalsTiny device the size of USB stick slots snugly on to back of a smartphoneResults are then delivered to an app, which tells patient if they have a normal or abnormal heart rhythm 
 Questions:With AF, blood can pool and clots can form inside the heart, which, if left untreated, can make the patient five times more likely to suffer an _-related stroke. (A) AliveCor (B) ECG (C) Britons (D) USB
A: 
(A)